WOS - Web of Science
Permanent URI for this collectionhttps://acikarsiv.thk.edu.tr/handle/123456789/2552
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Publication On- and off-optical-resonance dynamics of dielectric microcylinders under plane wave illumination(OPTICAL SOC AMER, 2015) Mahariq, I.; Kurt, H.; TOBB Ekonomi ve Teknoloji University; Turkish Aeronautical Association; Turk Hava Kurumu UniversityWe explore the on-resonance and off-resonance optical response of dielectric cylinders excited by normal incident plane waves. Both the analytical method, based on Mie theory, and the numerical method, implemented with the spectral element method, are undertaken in the study. We demonstrate that the whispering gallery mode characteristic of resonance behavior is strongly dependent on the refractive index and radius changes. Detuning of either parameter deteriorates the resonance action and creates yet another exciting phenomenon known as photonic nanojets. The subwavelength light focusing property can be associated with nanojets, and engineering the parameters yields strong field confinement and slowly diffracting beam propagation. The current work investigates the optical properties of the dielectric microcylinders at close proximity to the resonance condition. Both strong field focusing associated with photonic nanojets and enhanced field localization linked with the resonance condition are desired for photon manipulation scenarios in nanophotonics. (C) 2015 Optical Society of AmericaPublication Characterizations of self-assembly of peptides and self-assembled peptide nanonetworks(AMER CHEMICAL SOC, 2014) Cinar, Goksu; Tekin, Emine Deniz; Guler, Mustafa Ozgur; Tekin, Emine Deniz; Ihsan Dogramaci Bilkent University; Turk Hava Kurumu University; Turkish Aeronautical AssociationPublication Reduce Power Losses and Improve Voltage Level by Using Distributed Generation in Radial Distributed Grid(IEEE, 2017) Sajir, Husham; Rahebi, Javad; Abed, Amir; Farzamnia, Ali; Turkish Aeronautical Association; Turk Hava Kurumu University; Universiti Malaysia SabahServices provided by distributed generation (DG) to power generation and transmission systems have become an urgent necessity due to increase in load demand in recent years. These services include bridging the lack of central generation, increase the reliability of the network, reduce the inactive power in the system, and improve the margin of voltage for the network. On the other hand, the use of energy sources and diversification in the production of electric power. The voltage fluctuation on the end of consumer requires fast-paced strategic solutions and one of these solutions is the distributed generation. They contribute to the control of the voltage fluctuation to have a positive role in the work of the on-load tap changer (OLTC) which is sometimes unable to compensate for the lack of value of the voltages supplied from the source. The main contribution of this work is the introduction particle swarm optimization (PSO) algorithm to simulate a power system using the MATPOWER 6.0 as a tool box and one distributed generation to support the voltage profile. The results were positive as the system was simulated before the generator was entered into the network and the voltage measurement results were Low and after the input of the generator to the distribution network recorded a clear improvement in the voltage profile.Publication Peak to Average Power Ratio (PAPR) Reduction in OFDM for Optic Communications based on Conventional Selected Mapping(INT JOURNAL COMPUTER SCIENCE & NETWORK SECURITY-IJCSNS, 2019) Awad, Ousama M. Abdulwanes; Kilicaslan, Muhammed Fatih; Rahebi, Javad; Kastamonu University; Turkish Aeronautical Association; Turk Hava Kurumu UniversityOFDM is a modulation technique that utilizes the optic communication band efficiently by dividing the high-speed information sequence into parallel arms and lifting the frequency selectivity of the multi-carrier channel at the same time and using vertically selected carriers at the same time. Selected mapping is an accurate method for reducing peak to average power ratio from orthogonal frequency division multiplexing. A fundamental weakness of selected mapping is the high computational complexity. To reduce the complexity of the selected mapping, the real and imaginary part of the orthogonal frequency division multiplexing signals is treated separately. Numerical sequences and even real and imaginary elements are obtained using Fourier transform properties. More candidates are produced with a different combination of all the following sequences. The proposed scheme produces less computational complexity using the IFFT algorithm for M4 equations only. The simulation results show that the proposed design reduces the good performance of peak to average power ratio and also reduces computational complexity compared with the selected mapping design.Publication Strong field enhancement of resonance modes in dielectric microcylinders(OPTICAL SOC AMER, 2016) Mahariq, Ibrahim; Kurt, Hamza; Turk Hava Kurumu University; Turkish Aeronautical Association; TOBB Ekonomi ve Teknoloji UniversityA loss-free compact dielectric microcylinder acting as an optical resonator is studied in the present work by means of the spectral element method. A specific whispering gallery mode (WGM) supported by the structure is constantly tracked under the same type of illumination while varying the diameter of the resonator between similar to 5 lambda and 8 lambda (lambda = wavelength of light). The parameter space of the optical resonator informs us that it is possible to have either a larger radius of microcylinder with a smaller refractive index or a smaller radius of microcylinder with a larger refractive index value. Two different scenarios are also considered in the current study in order to verify the strong field confinement; one is under Bessel beam illumination conditions and the other is the introduction of nonhomogeneity in the material forming the cylinder. Strong power enhancement up to 3 orders of magnitude is attainable with small microcylinders. While the refractive index changes from 1.50 to 2.25, the corresponding radius utilizing the same type of WGM has to be carefully captured with fine tuning. It is imperative to increase the number of significant digits from 3.9380 lambda to 2.6600939 lambda in order not to miss such huge field enhancement phenomena. Standard resonance condition for constructive interference does not give us targeted parameters. The study may pave the way toward a new technique to detect nanoscale objects below the diffraction limit and may contribute to a new ultramicroscopy technique for detecting single molecules by low-threshold microcavity lasers. Additionally there are nonlinear optics applications. (C) 2016 Optical Society of AmericaPublication A Novel Smart Fatigue Damage Sensor for Structural Health Monitoring of Critical Components of Structures(IEEE, 2016) Kaplan, Halit; Ozkul, Tarik; Turk Hava Kurumu University; Turkish Aeronautical Association; American University of SharjahIn this paper we present the details of a novel fatigue sensor designed to monitor health status of mission critical mechanical systems. The designed fatigue sensor is unique in the respect that it senses fatigue related degradation before the actual catastrophic failure happens and gives ample time for replacement of the fatigued part. The electronics of the sensor is wireless enabled and can be made to work without any power source so that it can be attached to critical structural members of the structure during manufacture and can be left in place until the part is replacedPublication Experimental and numerical investigation into strength of bolted, bonded and hybrid single lap joints: Effects of adherend material type and thickness(ELSEVIER SCI LTD, 2018) El Zaroug, M.; Kadioglu, F.; Demiral, M.; Saad, D.; Turk Hava Kurumu University; Turkish Aeronautical Association; Ankara Yildirim Beyazit UniversityIn line with the developments in advanced engineering applications such as aerospace and automotive industries, the techniques of joining similar and dissimilar materials have become a crucial issue, i.e. the need for a stronger joint has significantly grown. Compared to conventionally used bolted, riveted and pinned joints, adhesively bonded joints have been increasingly used due to its improved fatigue life and damage tolerance and lower structural weight, especially the case when relatively thin adherends are used. Alternatively, hybrid joints, combination of two or more joining techniques, are presently investigated to create a joint with higher strength than those gained from one technique. In this study, we compared mechanical performance of bolted, bonded and hybrid single lap joints subjected to the tensile loading using three different adherend thicknesses and two different adherend materials with different mechanical behaviors, such as yield and tensile strength and ductility. To this end, a combined experimental and numerical study was performed. In finite element simulations, cohesive zone, ductile and shear damage models were used to model the damage initiation and evolution for the adhesive film layer (AF163-2K), aluminium adherend (AL6061 and AL7075) and the steel bolt materials, respectively. Force displacement curves, the amount of energy absorbed and failure history for each configuration tested, were analysed extensively to elucidate the strength of various joints.Publication A Generic, Multi-Period and Multi-Partner Cost Optimizing Model for Cloud-Based Supply Chain(IGI GLOBAL, 2016) Akyuz, Goknur Arzu; Rehan, Mohammad; Turkish Aeronautical Association; Turk Hava Kurumu University; Atilim UniversityCloud technology in a multi-enterprise, collaborative context is one of the most promising topics at IT-Supply Chain (SC) intersection. Cloud comes with well-proven advantages and cost savings; enabling collaboration and business intelligence. Cloud transition is still on-going with individual enterprise-level transitions. However, collaborative paradigm dictates that entire network well-being is to be considered over enterprise-level concerns. Thus, handling the transition of a single enterprise is not sufficient for strategic network leverage. Planning and managing across multiple enterprises is required, taking into consideration various cost items and budget constraints. In this study, a multi-period multi-partner cost-optimizing model is developed for network-level management of cloud transition for a SC. The model produces an optimal transition plan, indicating timing of the transition for each partner to obtain the maximum cost savings across network over a specified planning horizon. The model proposed is generic, flexible and customizable for different sectors/settings.Publication A fuzzy approach for the reviewer assignment problem(PERGAMON-ELSEVIER SCIENCE LTD, 2014) Das, G. Sena; Gocken, Tolunay; Turkish Aeronautical Association; Turk Hava Kurumu University; Adana Alparslan Turkes Science & Technology UniversityAssignment of experts to project proposals is a significant task for funding agencies which have to assess the potential value of the research and development (R&D) projects through peer review. The problem is known as reviewer assignment problem and has real-world applications in funding agencies, conferences and research journals. Given a set of experts and a set of proposals; the problem can be defined as assigning the most suitable experts to the proposals under some constraints, which are generally encountered by funding agencies. In this study, a fuzzy model is offered to solve the reviewer assignment problem. The objective of the model is to maximize the total matching degree of assigned experts under some constraints such as cost of forming a panel and the size of a panel. The matching degrees are defined using linguistic variables to denote the expertise of each expert with respect to each proposal. The fuzzy mathematical model, which also takes into account different constraints related to the problem, is solved via the selected fuzzy ranking methods namely; the signed distance method and the method of ranking fuzzy numbers with integral value. The solution of an example problem - inspired from a real-life situation with both of the mentioned methods revealed the effectiveness of the solution approach. It is believed that the use of the offered fuzzy approach could improve the accuracy of the decisions made by funding agencies. (C) 2014 Elsevier Ltd. All rights reserved.Publication Evolutionary parallel extreme learning machines for the data classification problem(PERGAMON-ELSEVIER SCIENCE LTD, 2019) Dokeroglu, Tansel; Sevinc, Ender; Ted University; Turk Hava Kurumu University; Turkish Aeronautical AssociationThis study proposes an Island Parallel Evolutionary Extreme Learning Machine algorithm (WE-ELM) for the well-known data classification problem. The ELM is a fast and efficient machine learning technique with its single hidden layer feed-forward neural network (SLFN). High prediction accuracy and learning speed of the ELM make it an elegant tool for the fitness calculation process of the evolutionary algorithms. The IPE-ELM algorithm combines the evolutionary genetic algorithms (for feature selection), ELM machine learning technique (for prediction accuracy calculation), parallel computation (for faster fitness evaluation), and parameter tuning (activation function selection and the number of hidden neurons) for the solution of this important problem. Each ELM that runs at a different processor selects one of four different activation functions (Sine, Cosine, Sigmoid and Hyperbolic Tangent) and uses a randomized number of hidden neurons to achieve higher prediction accuracy. The proposed algorithm provides high quality results with its (near)-linear scalability behavior. The IPE-ELM algorithm is compared with state-of-the-art data classification algorithms by using UCI benchmark datasets and significant improvements are reported in terms of prediction accuracy with reasonable execution times. The scalable IPE-ELM algorithm can be reported as the first island parallel evolutionary classification algorithm with its high prediction accuracy results that outperforms state-of-the-art algorithms in literature.